Hi Aasai,
I’m sorry about the inconvenience, but I would like to confirm if you are using the Office 365 Professional and Small Business subscription?
To clarify the issue, does the Site Collection features listed for your tenant are as the following?
If this is the case, then, you are in a normal situation. For Small Business plan SharePoint Online, some workflow actions are not available. For more details, you can refer to the following KB:
http://support.microsoft.com/kb/2539387
According to the KB, to resolve this issue, you must use a supported action in the workflow, or you must use Office 365 for enterprises.
Hope the above information helps you!
Thanks,
Evan Zhang